Hydroformylation of styrene in supercritical carbon dioxide with fluoroacrylate polymer supported rhodium catalysts

Rhodium catalysts, bound to a fluoroacrylate copolymer backbone through phosphine ligands, are synthesized and shown to be soluble and active in supercritical carbon dioxide. Hydroformylation of styrene is studied using this catalyst at two different temperatures (323 and 348 K) and three different pressures (172, 207, and 241 bar). The initial mole fraction of styrene was 4.13 x 10(-4), styrene to Rh molar ratio was 200, and hydrogen and carbon monoxide to styrene molar ratio was 160. Conversions up to almost 100% and branched aldehyde selectivities of 95-100% were obtained at most reaction conditions. A kinetic model is proposed based on a dissociative mechanism, which starts by dissociation of a CO ligand to produce RRh(CO)(2)L-2. Then coordination of an olefin, insertion of hydrogen, and coordination of CO generates the alkylrhodium complex followed by CO insertion to generate the acyl complex. Finally, reductive elimination forms the aldehyde. Oxidative addition of hydrogen is proposed as the rate-control ling step. (C) 2004 Published by Elsevier B.V.